The present invention relates to a system for controlling the rotation of the body of a railway vehicle about its longitudinal axis for the purpose of reducing the value of non-compensated acceleration acting in a transverse direction on passengers in the vehicle.
Variable aspect railway vehicles are known which, when travelling around a bend, allow the body to rotate about a longitudinal axis with respect to the track. This rotation, which can take place in a spontaneous or a controlled manner, makes it possible partly or totally to compensate for the component of the centrifugal force which acts on the passengers, by means of a component of the passengers'weights. Therefore, when a variable aspect vehicle travels along a curved path, a residual acceleration acts in a transverse direction on the passengers, which acceleration is defined as non-compensated acceleration and which is therefore equal to the difference between the components of centrifugal acceleration and gravitational acceleration in the said transverse direction.
The rotation of the body of the railway vehicle can take place in a spontaneous manner under the action of the forces of centrifugal inertia acting on the centre of gravity of this body, which, by means of suitable linkages, causes rotation of the body itself towards the inside of the curve. This system has the disadvantage of imparting to the body an acceleration which is too slow because of its high moment of inertia to rolling movement and because of the modest value of the couples thus generated. Therefore with this mode of operation the equilibrium position cannot be reached within the short time which is available during the transition between rectilinear movement and the full curve of the bend. It therefore happens that the compensation of the centrifugal force is insufficient along the connection portion and, as a consequence of this, the passengers can be subject to an intense (if relatively short) jolt and to an accentuated oscillation of the transverse acceleration which lasts into the bend and which can be very annoying. Both of these unfavourable effects limit the maximum admissable angle of rotation of the body to modest values (of the order of 3.degree.-4.degree. ) and therefore reduce to relatively limited values (of the order of 10-15%) the maximum increase of speed in bends.
For this reason the controlled or active system of rotation predominates, in which, by providing sufficiently powerful servo-controls, it is possible to move the body with all the necessary speed and make this perform the rotation smoothly and quickly. The operation of the servo-controls was initially achieved by a device sensitive to the transverse acceleration on the body itself, such as, for example, a pendulum having a longitudinal axis or an accelerometer fitted to the body; subsequently one or more accelerometers fitted to the carriage or to the carriages of the vehicle were used as an alternative.
Since with this system there was no possibility of distinguishing if the transverse accelerations to which the device was subjected were due to centrifugal force or were disturbances caused by irregular motions of the vehicle (in particular the phenomenon of rocking almost always present in the operation of railway vehicles) sometimes untimely interventions occurred.
To avoid this disadvantage it was necessary to fit a filter either to the movement of the pendulum or to the accelerometric signal generated by the said device; this filter acts at very low frequency and causes a delay in the transmissions of the control used for rotation, and a reduction in the time available to perform the change in aspect, resulting in an unpleasant oscillation in the residual transverse acceleration on the passengers. For the purpose of underlining the importance of the problems which arise for controlling the body aspect it must be borne in mind that at 200 kilometers per hour a parabolic transition section of 100 meters is traversed in about 2 seconds and that within this time it is necessary to perceive the presence of the curve, actuate the servo-control, accelerate the body, cause this to perform the entire rotation, slow and stop in the inclined position.
In Italian Patent No 920358 by the same applicant, filed Feb. 9, 1971, there is described a body rotation control system for a railway vehicle which makes it possible to detect, with a minimum delay, the beginning and end of the linking sections both at the beginning and the end of a bend in the railway track travelled by the vehicle, even if the track itself is elevated; this system further determines, in a timely and correct manner, the rotation of the body necessary to compensate the transverse acceleration. The system substantially comprises a gyroscope operable to generate a signal indicative of the angular velocity of rotation of the vehicle about is longitudinal axis, an integrator operable to generate a signal indicative of the angle of rotation of the vehicle about the said axis and a threshold adapted to allow the passage of this signal only when this exceeds a predetermined value in such a way as to give rise to a true and proper switch device adapted to emit an activation signal for the actuator displacing the body only when the angle of rotation of the vehicle exceeds a desired value.
The control system described was able to operate quickly and in a timely manner only if the track was elevated at the connector section (that is to say only if one of the rails is located at a different height with respect to the other) linking the rectilinear section and the bend. Otherwise, that is to say if the connector section was not elevated, it was not able to recognise the actuation phases.
Incorrect operation was furthermore encountered in cases in which the increase in the elevation varied with a different law from that with which the curvature of the track varied and, therefore, in the case of S-shape elevated connector links, connector links having double curvature or connector links having differently accentuated curves.